1. Field of the Invention
The present invention relates to a method of adjusting idling revolution in the engine of a vehicle by the feed-back control of the idling revolution.
2. Discussion of Background
Description will be made as to a conventional idling adjusting method with reference to FIG. 6. In FIG. 6, a reference numeral 1 designates an engine and a numeral 2 designates an intake air pipe. A throttle valve 3 is provided in the intake air pipe 2, and a by-pass passage 9 is connected to the intake air pipe 2 so as to by-pass the throttle valve 3 between the upstream side of the throttle valve 3 and the downstream side of it. The by-pass passage 9 comprises a main by-pass passage 91 and an auxiliary by-pass passage 92 which are arranged in parallel to each other. The main by-pass passage 91 includes an intake air control valve which controls the sectional surface area of the main by-pass passage. The intake air control valve may be a solenoid valve 8 having a linear characteristic. An adjusting screw 4 is provided in the auxiliary by-pass passage 92 so as to adjust an air quantity in the auxiliary by-pass passage by adjusting the sectional surface area of the passage. The solenoid valve 8 is to be controlled and driven by an output from a driving unit 7.
A gear wheel 41 is attached to a rotary shaft in the engine 1 so that the gear wheel 41 is rotated in association with the revolution of the engine 1. The revolution of the gear wheel 41 is detected by a revolution number sensor 42. An engine revolution number n.sub.E detected by the revolution number sensor 42 through the revolution of the gear wheel 41 is output to an error amplifying device 61. The error amplifying device 61 also receives a target revolution number n.sub.T from a target revolution number generating device 5, and it generates an error .DELTA.n of the signal n.sub.T to the signal n.sub.E so as to output the error signal to a revolution number adjusting device 62.
The target revolution number generating device 5 is to generate a predetermined target revolution number signal n.sub.T in response to various conditions such as a temperature of engine, or to generate a target non-load revolution number signal n.sub.T at the time of warming-up of the engine. The revolution number adjusting device 62 is to receive the output of the error amplifying device 61 and to output a revolution number correction signal Sc in the direction which will eliminate the error .DELTA.n by a proportional action, an integral action or a derivative action.
A reference controlled quantity output circuit 11 outputs a reference control signal S.sub.T indicative of a reference controlled quantity (a fixed value) so that the engine revolution number n.sub.E approaches the target revolution number n.sub.T. The reference control signal S.sub.T of the reference controlled quantity output circuit 11 and the output signal S.sub.c of the revolution number adjusting device 62 are added in an adder 13, and the adder 13 outputs a signal obtained by an adding operation. The output S.sub.T +S.sub.c of the adder 13 is supplied to a limiter 12. The limiter 12 outputs a signal in which the output signal S.sub.T +S.sub.c is limited in a predetermined range. The output of the limiter 12 is supplied to the driving unit 7, and the driving unit 7 supplies a driving signal to the solenoid valve 8 so that it is operated with a duty cycle in response to the input signal. The solenoid valve 8 is controlled by the driving signal so that a cross-sectional area of the by-pass passage 9 is increased or decreased so that an air quantity passing therethrough is increased or decreased.
The operation of the conventional idling adjusting method will be described.
When an error .DELTA.n of revolution number takes place, the revolution number adjusting device 62 is actuated, and it generates a revolution number correction signal S.sub.c. The revolution number correction signal S.sub.c has a tendency to reduce the value of the error signal .DELTA.n generated from the error amplifying device 61, and when the error signal value .DELTA.n becomes the smallest, the value is fixed. The output signal S.sub.c of the revolution number adjusting device 62 is added to the output signal S.sub.T of the reference controlled quantity output circuit 11 in the adder 13, and the value obtained by adding is supplied to the limiter 12. The output of the limiter 12, which is limited to a predetermined range, is supplied to the driving unit 7 so that the output signal is converted into a driving signal for the solenoid valve 8.
Adjustment of the device as shown in FIG. 6 will be described. Assuming that the adjustment is made under conditions that the throttle valve 3 is at an idling position and the engine 1 is sufficiently warmed. A correction value output circuit 20 converts the revolution number correction signal S.sub.c generated from the revolution number adjusting device 62 into a duty signal having a characteristic as shown in FIG. 7, and the duty signal is output to a meter 21 located externally. The meter 21 may be a volt meter which shows a scale corresponding to average voltage. An operator adjusts an intake air quantity with an adjusting screw 4 provided in the by-pass passage 9 so that the indication of the meter corresponds to a 50% value of duty cycle. By such adjustment, the revolution number correction signal Sc becomes 0, and an error in revolution number, which may result due to various kinds of cause including the case that an intake air quantity is reduced by the clogging of the solenoid valve 8, can be adjusted.
In the conventional idling adjusting method for the engine of a vehicle, there is found a disadvantage as follows. When adjustment of the adjusting screw is made during an idling operation at a high altitude where the density of air is thin, the degree of opening after the adjustment is greater than that at a low altitude. Accordingly, when a vehicle adjusted for idling at a high altitude moves to a low altitude it is difficult to maintain a target revolution number because the density of air at the low altitude is thicker than that of the high land. Namely, even though the solenoid valve 8, i.e., the intake air control valve is to be closed, it is impossible to control the intake air quantity because there exists the lower limit of a range of control, whereby an idling revolution number is higher than the target revolution number, hence, fuel consumption efficiency becomes poor.